SUMMARY OF THE PRESENT INVENTION
This invention relates to a device for holding a corrugated paperboard test specimen during an edge compression test on the specimen.
An edge compression test on a corrugated paperboard specimen is performed to test the compressive strength of the specimen in planes parallel to the major surfaces of the specimen. Commonly the test specimen is a square section cut from a representative corrugated paperboard panel used in the manufacture of paperboard (fibreboard) shipping cartons. The square test section typically measures two inches on a side (which provides a specimen face area of four square inches).
The edge compression test is performed by standing the test specimen upright (on edge) within a testing machine so that an upper edge of the specimen is presented to an upper platen in the machine, and a lower edge of the specimen is presented to a lower platen in the machine. The lower platen is powered upwardly toward the upper platen at a controlled rate so that compressive forces are applied to the specimen along vertical planes paralleling the major surfaces of the upright test specimen.
The test specimen is usually arranged so that the flutes of the reinforcement corrugations in the specimen are oriented vertically, i.e., parallel to the directions of the applied compressive forces. This is done so that the corrugated paperboard will be tested in the direction of maximum strength, i.e., parallel to the flutes.
In order to hold the test specimen in a precise vertical upright position in the test machine during the edge compression test, it is the usual practice to mount the specimen in a holder while the test is being performed. The holder keeps the specimen precisely vertical during the test so that the applied forces are applied to the specimen in the proper (desired) direction. This ensures repeatability of the testing process, whereby test results with different samples can be compared with the necessary quality assurance and confidence.
The present invention relates to a holder for a corrugated paperboard test specimen while the specimen is being tested for edgewise compressive strength. The preferred holder construction comprises a lower clamp means for holding a lower end portion of the specimen, an upper clamp means for holding an upper portion of the system, and an upright slide mechanism for slidably supporting the upper clamp means, whereby the application of a vertical compressive force to the upper and lower clamp means subjects the specimen to a potentially destructive vertical test force.
The upper and lower clamp means are designed so that the clamped areas of the specimen are subjected to clamp forces that are sufficient for the desired clamp action, while at the same time not producing any undesired deformation of the specimen surface. Such deformation is undesirable in that the specimen is thereby weakened so as to adversely affect the test result or its meaning.
A sufficient clamp force is necessary to avoid slippage between the clamp mechanism and the specimen. Such slippage would adversely affect the test result in that vertical strain produced by the load forces would appear as a squashing or indentation of the specimen end edges, rather than deflection of the unclamping areas of the specimen. The machine readings would then not be representative of the edgewise compressive strength of the specimen.
The preferred specimen holder embodying the invention utilizes clamp mechanisms wherein clamp pads are biased by coil springs that produce a consistent uniform clamp force, sufficient to prevent slippage of the specimen without deforming the specimen surface, in contact with the clamp mechanisms. The clamp surfaces are preferably treated or formed to achieve a relatively high coefficient of friction between the clamp surfaces and the test specimen surfaces; the aim is to prevent vertical slippage between the specimen and the clamp mechanisms, without employing excessively high clamp forces, as might deform the specimen surfaces.
The holder of the present invention is designed so that the clamp pads are easily retracted away from the associated vertical clamp walls, whereby test specimens can be quickly and easily inserted into the clamp mechanisms without undue effort or precision. Each clamp pad has a horizontal rod extending into a channel spaced from the associated vertical clamp wall; a manually rotatable nut is threaded onto each rod within the associated channel. By rotating each nut in a particular direction it is possible to retract the associated clamp pad. By rotating each nut in the opposite direction the associated rod is moved linearly to enable the respective clamp pad to advance against the test specimen; a coil spring surrounding each rod exerts a clamp force on the associated pad.
The holder is designed for easy manual opening and closing of the upper and lower clamp mechanisms. The clamp mechanisms are constructed so that the clamp force is essentially constant and independent of the thickness of the test specimen. Variations in the test specimen thickness do not affect the clamp force.
Further features and advantages of the test specimen holder will be apparent from the attached drawings and accompanying description of an illustrative embodiment of the invention.
In summary, and in accordance with the above discussion, the foregoing objectives are achieved in the following embodiments:
1. A holder for a corrugated paperboard test specimen that is to be tested for edgewise compression strength:
said holder comprising a support mechanism having a vertical slideway; PA1 a lower specimen clamp means carried by said support mechanism; and PA1 an upper specimen clamp means slidably mounted on said slideway for vertical movement toward or away from said lower clamp means. PA1 each said manual means comprises a linear rod extending horizontally from the respective pad, and a rotary nut threaded onto each respective rod, whereby manual rotation of the rod moves the rod and associated pad. PA1 said vertical slideway comprising a guide element located in said recess; PA1 said upper clamp means having a slide element slidably mounted on said guide element for vertical movement; and PA1 said lower clamp means comprising a vertical wall secured to said vertical block, a horizontal wall extending from said vertical wall, and a movable pad slidably mounted on said horizontal wall for movement toward or away from said vertical wall. PA1 said nut being manually rotatable to move said first rod and the associated pad away from said first vertical wall; and PA1 said coil spring having one end thereof abutting said first pad to normally bias said first pad toward said first vertical wall in the absence of an opposing force by said first nut. PA1 said second nut being manually rotatable to move said second rod and the associated pad away from said second vertical wall; and PA1 said second coil spring having one end thereof abutting said second pad to normally bias said second pad toward said second vertical wall in the absence of an opposing force generated by said second nut. PA1 said vertical faces having friction gripper properties to prevent the test specimen from slipping on said vertical faces.
2. The holder, as described in paragraph 1, wherein each said clamp means comprises a vertical clamp surface adapted to engage one face of a test specimen, a horizontally movable pad adapted to engage the other face of the test specimen, and spring means biasing said pad toward the associated clamp surface.
3. The holder, as described in paragraph 2, wherein each said clamp means further comprises a manual means for moving the respective pad away from the associated clamp surface to permit insertion of a test specimen into the upper and lower clamp means.
4. The holder, as described in paragraph 2, wherein each said clamp means further comprises a manual means for moving the respective pad away from the associated clamp surface to permit insertion of a test specimen into the upper and lower clamp means; and
5. The holder, as described in paragraph 4, wherein each said spring means comprises a coil spring encircling the respective linear rod.
6. The holder, as described in paragraph 1, wherein said support mechanism comprises a vertical block having a vertical recess;
7. The holder, as described in paragraph 6, wherein said upper clamp means comprises a second vertical wall affixed to said slide element, a second horizontal wall extending from said second vertical wall, and a second movable pad slidably mounted on said second horizontal wall for movement toward or away from said second vertical wall.
8. The holder, as described in paragraph 7, wherein said lower clamp means further comprises a first channel secured to said first horizontal wall, a first horizontal rod extending from said first pad through said channel, a first coil spring encircling said first rod in the space between said first pad and said channel, and a first rotary nut threaded onto said first rod within said first channel;
9. The holder, as described in paragraph 8, wherein said upper clamp means further comprises a second channel secured to said second horizontal wall, a second horizontal rod extending from said second pad through said second channel, a second coil spring encircling said second rod in the space between said second pad and said second channel, and a second rotary nut threaded onto said second rod within said second channel;
10. The holder, as described in paragraph 9, wherein said first and second vertical walls have vertical faces adapted to grip one face of a test specimen, and said first and second pads have vertical faces adapted to grip the other face of a test specimen; and
11. The holder, as described in paragraph 1, wherein each said clamp means comprises a vertical clamp surface adapted to engage one face of a test specimen, a horizontally movable pad adapted to engage the other face of the test specimen, and spring means normally biasing said pad toward the associated vertical clamp surface; and said vertical clamp surfaces and said pads having frictional grip properties to prevent the test specimen from vertical slippage.
12. The holder, as described in paragraph 1, wherein each said upper and lower clamp means comprises a movable pad and a facing vertical wall that cooperatively form a side access slot; and each said clamp means being openable by a horizontal movement of the respective pad away from the associated vertical wall, whereby the side access slots are widened to permit insertion of a test specimen into the clamp means.